High-purity CO₂ rather than dilute CO₂ (15 vol %, CO₂/N₂/O₂ = 15:80:5, v/v/v) similar to the flue gas is currently used as the feedstock for the electroreduction of CO₂, and the liquid products are usually mixed up with the cathode electrolyte, resulting in high product separation costs. In this work, we showed that a microporous conductive Bi-based metal–organic framework (Bi-HHTP, HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) can not only efficiently capture CO₂ from the dilute CO₂ under high humidity but also catalyze the electroreduction of the adsorbed CO₂ into formic acid with a high current density of 80 mA cm^–2 and a Faradaic efficiency of 90% at a very low cell voltage of 2.6 V. Importantly, the performance in a dilute CO₂ atmosphere was close to that under a high-purity CO₂ atmosphere. This is the first catalyst that can maintain exceptional eCO₂RR performance in the presence of both O₂ and N₂. Moreover, by using dilute CO₂ as the feedstock, a 1 cm^–2 working electrode coating with Bi-HHTP can continuously produce a 200 mM formic acid aqueous solution with a relative purity of 100% for at least 30 h in a membrane electrode assembly (MEA) electrolyzer. The product does not contain electrolytes, and such a highly concentrated and pure formic acid aqueous solution can be directly used as an electrolyte for formic acid fuel cells. Comprehensive studies revealed that such a high performance might be ascribed to the CO₂ capture ability of the micropores on Bi-HHTP and the lower Gibbs free energy of formation of the key intermediate *OCHO on the open Bi sites.

中文翻译：

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有效捕集稀二氧化碳并将其电还原成高纯浓甲酸水溶液


高纯度 CO ₂ 而不是稀释 CO ₂ （15 vol %，CO ₂ /N ₂ /O ₂ 的原料，液体产物通常与阴极电解液，导致产品分离成本较高。在这项工作中，我们证明了微孔导电Bi基金属有机骨架（Bi-HHTP，HHTP = 2,3,6,7,10,11-六羟基苯并菲）不仅可以有效捕获CO ₂ 在高湿度下从稀 CO ₂ 中分离出来，而且还能在 80 mA cm 的高电流密度下催化吸附的 CO ₂ 电还原为甲酸 ^–2 在 2.6 V 的极低电池电压下，法拉第效率为 90%。重要的是，稀 CO ₂ 气氛中的性能接近于高纯度 CO ₂ 下的性能气氛。这是第一种在 O ₂ 和 N ₂ 存在的情况下仍能保持出色的 eCO ₂ RR 性能的催化剂。此外，以稀CO ₂ 为原料，1 cm的Bi-HHTP ^–2 工作电极涂层可以连续生产200 mM的甲酸水溶液，相对纯度为100 % 在膜电极组件 (MEA) 电解槽中至少 30 小时。该产品不含电解质，这种高浓度、高纯度的甲酸水溶液可直接用作甲酸燃料电池的电解质。综合研究表明，如此高的性能可能归因于Bi-HHTP上微孔的CO ₂ 捕获能力以及开放Bi位点上关键中间体*OCHO较低的吉布斯形成自由能。